The present invention relates to a control appliance, in particular a steering system for motor vehicles, having a manually actuated handling device, such as a steering wheel, and control elements, such as steered wheels, connected thereto by a drive connection, and having a motorized drive appliance which is selectively connected to the control elements, which can be automatically controlled in either an open-loop or closed-loop manner and which permits the control elements to be actuated autonomously.
U.S. Pat. No. 3,073,407 describes a motor vehicle steering system which operates fully automatically during certain manoeuvres for parking the motor vehicle because a motorized drive appliance with automatic control actuates the steering system. In this system, the steering wheel also rotates to correspond with the particular steering manoeuvres, i.e. the driver can "observe" how the steering operates.
In addition, it is known that motor vehicles, in particular passenger cars, can have the vehicle steering system configured such that under certain driving conditions, particularly with side-wind perturbations by way of example, an automatic steering intervention takes place in order to stabilize the vehicle. In order to avoid the driver being irritated or disturbed by the automatic steering intervention, an automatically operating rear-wheel steering system is usually provided, whereas the steering system actuated by the driver acts on the front wheels. The automatic steering intervention can therefore take place without the driver feeling any motions or forces at the steering wheel, with the exception of the particular steering forces and motions caused by road effects. It is, however, also fundamentally known to undertake automatic steering interventions by way of the front wheels alone or additionally. The driver can, however, be annoyed when the steering wheel is also moved by the automatic steering intervention.
A so-called derivative steering system is described in DE 38 30 654 Al. The characteristic feature of this system is that the transmission ratio between the setting motion of the steering wheel and the change in steering angle of the steered wheels caused thereby changes as a function of the setting rate of the steering wheel. The steering wheel drives via an input shaft, for this purpose, the sun wheel of an epicyclic gear configured as a differential gear. An output shaft torsionally connected to the internal teeth gearwheel or ring gearwheel of this gear controls the vehicle steered wheels. A motor controlled by an automatic closed-loop control appliance drives a spindle which forms a second input to the epicyclic gear and is in engagement with the planet carrier, which has external teeth. The transmission ratio between the input shaft and the output shaft is correspondingly determined by the rotational direction and the rotational speed of the motor. If the steering wheel or the input shaft is kept at rest, the steering angle of the vehicle steered wheels does not change, as is typical of a derivative steering system.
A control system, provided particularly for heavy road rollers, is described in GB-A 297 659 and permits switching between two types of operation. In one type of operation, the steering wheel acts directly and without any motorized support on the steering elements of the vehicle, usually a steerable roller. The steering wheel is then mechanically drive-connected to the steering elements. In the other type of operation, the direct mechanical connection between the steering wheel and the steering elements is separated because a claw coupling provided for this purpose takes up its open state in this type of operation. At the same time, the steering wheel controls a control coupling which connects a continuously running drive motor in different ways to the control elements such that, depending on the rotational direction of the steering wheel, the control elements are adjusted in one direction when the steering wheel is actuated in one rotational direction and are adjusted in the opposite direction when the steering wheel is actuated in the other rotational direction.
An object of the present invention is to provide a novel control system of the aforementioned type with, on one hand, the highest safety requirements being satisfied, and, on the other hand, irritation or annoyance of the operating personnel or the driver and incorrect manoeuvres caused thereby being avoided as far as possible.
This object has been achieved according to the present invention, by providing that a permanently effective positive connection between an input part and an output part of the drive connection can, in effect, be separated. The drive appliance actively adjusts the output part or subjects it to a torque and, while overcoming a self-locking device, effects a disconnection, which is prevented by the self-locking device when the drive appliance is separated from its energy supply, of the input part from the output part.
The present invention therefore provides that the handling device or the steering wheel is in a continually effective connection with the control elements (or steered wheels) by way of the positive connection, which is preferably configured as a permanently effective mechanical through-connection between the input part and the output part. The drive connection between the handling device or steering wheel and the control elements or steered wheels is only apparently separated in the case of automatic control or steering interventions.
This arrangement, on the one hand, gives the operating personnel or the driver "dominance" over the control or steering system. When the energy supply to the drive appliance is shut off, on the other hand, the operating behavior of a conventional control or steering system, i.e. a system without automatic control or steering intervention is provided immediately.
In accordance with a first advantageous embodiment of the invention, it is possible to provide that the input part and the output part are positively drive-connected by a sliding clutch or the like, which is expediently configured so that the forces and torques exerted on the control system or the steering system by the operating personnel or by the driver during normal operating phases can be readily transmitted. Furthermore, the input part and the output part are each provided with an automatically controllable drive which is not self-locking and by way of which the automatic control or steering intervention then takes place when required.
It is then expedient for the drive connected to the output part to effect control manoeuvres or steering manoeuvres whereas the drive acting on the input part holds it completely or almost at rest. For example, it is therefore advantageously possible to achieve the effect that the operating personnel or the driver notices the automatic control or steering intervention on the handling device or on the steering wheel by more or less slight reactions or motions of the handling device or of the steering wheel without, however, becoming uneasy or irritated by excessively strong reactions or motions, such as occur in the case of motion of the handling device or of the steering wheel corresponding to the particular control or steering intervention.
In a second advantageous embodiment of the invention, the input part and the output part are connected together by a self-locking motorized drive. Furthermore, a motorized drive which is not self-locking is arranged on the input part and/or on the output part. An automatic control or steering intervention, in which the handling device or the steering wheel remain substantially at rest or execute markedly reduced motions compared with the particular control or steering intervention, can then again take place by appropriate automatic actuation of the self-locking motorized drive and the drive, which is not self-locking, on the input part and/or on the output part.
When the drives are separated from their energy supply in this second embodiment, the input part and the output part can be positively connected together in a practically rigid manner via the self-locking drive which can be configured as a travelling wave electric motor to behave mechanically like a sliding clutch, and a non-self-locking motor which is connected in parallel therewith.
In an advantageous third embodiment of the present invention, a superimposed gear provided with two inputs and one output is arranged between the input part and the output part. One input of the superimposed gear is positively connected to the input part, its output is positively connected to the output part and its extra input is movable, via a motor, relative to a stationary part. The extra input is held stationary by the self-locking nature of the motor or gear parts connected thereto when the motor is separated from its energy supply. In addition, the input part and/or the output part is provided with a motorized drive which is not self-locking.
Here again, a control or steering intervention, in which the handling device or the steering wheel are not moved in a motorized fashion or are moved in a motorized fashion in a manner independent in principle from the control or steering intervention, can take place by appropriate control of the drives in this third embodiment.
In both the second and the third embodiment of the present invention, the arrangement of non-self-locking motorized drives on the output part and on the input part permit a mode of operation in which the self-locking drive between the input part and the output part and the motorized drive on the second input of the superimposed gear only have to overcome the resistance of the self-locking device. The two non-self-locking drives undertake the control or steering intervention and the motion or stationary condition of the handling device or the steering wheel which are, in effect, decoupled from the control or steering intervention.
A very high level of safety is provided by the three embodiments of the present invention because the handling device or the steering wheel remain in continuous drive connection with the control elements. Consequently, the operating personnel or the driver have the continuous possibility of manual intervention. Moreover, the automatic control of the drives need only continually check for fault-free behavior and need only separate the drives from the energy supply when a fault occurs. Conventional control or steering is then immediately available without the possibility of automatic intervention. Furthermore, emergency operation is still fundamentally possible when a drive fails.